The Menstrual Cycle

The Menstrual Cycle is the time from one menstruation (or period) to the next.

What drives the menstrual cycle?

The menstrual cycle is caused by hormonal changes in the body, which trigger ovulation (the release of an egg from the ovary) and later menstruation (the breakdown of the uterus lining). Because it is driven by fertility hormones, a woman will start having menstrual cycles from puberty until menopause.

The phases of the menstrual cycle

The menstrual cycle is composed of three different phases, with an average total length of 28 days, however this can be highly variable between women and may vary over time for one woman. About half of all women have a menstrual cycle of between 26 and 31 days, with the remaining having cycles either longer or shorter than this (about 10% of women have cycles longer than 45 days). Each cycle begins on the first day of full menstrual flow (your period) and ends on the day before you get your next period. Around the middle of your cycle, ovulation occurs, which triggers a number of changes in your body. The time before ovulation is called your follicular phase, and the time after ovulation is called the luteal phase.

What is ovulation?

Ovulation is the release of an egg from the ovaries, the event around which the whole menstrual cycle is driven. During the follicular phase, your body is preparing for the release of the egg and possible fertilisation of that egg. The length of the follicular phase can be quite variable, generally ranging from 12-17 days. During the luteal phase, which typically lasts a further 12-16 days, your body is preparing for implantation of the fertilised egg (embryo) into the womb lining (the endometrium).

When in the menstrual cycle am I fertile?

The menstrual cycle determines when you are fertile (are able to get pregnant). You are usually fertile for just a few days around the day of ovulation, as sperm must meet the egg before it dies, around 24 hours after ovulation.

Your cycle is regulated by hormones, the brain and your reproductive organs. Each cycle, your body prepares itself to support a potential pregnancy. As you approach ovulation each month, your uterus becomes more welcoming to sperm, allowing them to survive longer and swim to the egg; which increases your chances of getting pregnant.

If you have intercourse during your fertile days and fertilisation occurs between a sperm and the egg released that menstrual cycle, the resulting embryo may implant itself in your uterus, which will develop a thicker lining (or endometrium) and better blood circulation to support the growth of the embryo.

If fertilisation does not occur, no pregnancy is achieved during this particular menstrual cycle and hormonal changes will then trigger the thickened endometrium to slip away. This is the start of your menstruation (or period).

The DuoFertility programme will help you identify when you are most fertile, helping you to maximise your chances of getting pregnant. We’ll predict your fertile days in advance, allowing plenty of time to plan ahead.